Effects of Cohabitation on the Population Performance and Survivorship of the Invasive Mosquito Aedes albopictus and the Resident Mosquito Aedes notoscriptus (Diptera: Culicidae) in Australia.

The presence of Aedes albopictus (Skuse) in the Torres Strait of northern Australia increases the potential for colonization and establishment on the mainland. However, there is a possibility that native species that occupy the same habitats may influence the population performance of Ae. albopictus, potentially affecting the establishment of this species in Australia. Cohabitation experiments were performed with the endemic Aedes notoscriptus (Skuse), which has been found occupying the same larval habitats as Ae. albopictus in the Torres Strait and is the most widespread container-inhabiting Aedes species in Australia. The influence of environmental factors and cohabitation between the two species was examined using different climates, food resource levels, food resource types, and species densities. Survivorship proportions and a population performance index (λ') were calculated and compared. The consequences of increased Ae. notoscriptus densities were reduced survivorship and λ' for Ae. albopictus. Despite this, the mean λ' of Ae. albopictus and Ae. notoscriptus was consistently ≥ 1.06, indicating both species could increase under all conditions, potentially due to increasing conspecific densities negatively affecting Ae. notoscriptus. The outcomes from this study suggest that the preexisting presence of Ae. notoscriptus may not prevent the establishment of Ae. albopictus in Australia.

Field Comparison of Cyclopentanone Versus Carbon Dioxide as an Attractant for Adult Mosquitoes in Southeast Queensland, Australia.

Cyclopentanone is a saturated monoketone typically used as an intermediate in the manufacture of pharmaceuticals, biologicals, insecticides, and rubber chemicals. Recently, it has been demonstrated that cyclopentanone activates the cpA CO2 receptor neuron on the maxillary palp of mosquitoes, suggesting that it may be a viable alternative to CO2 as an attractant for mosquitoes. Furthermore, semifield experiments showed that traps baited with cyclopentanone attract Culex quinquefasciatus Say at a similar rate to those baited with CO2. We evaluated the field efficacy of cyclopentanone as an alternative to CO2 in Centers for Disease Control (CDC) light traps and counterflow geometry (CFG) traps commonly used to collect mosquitoes in surveillance programs. Three pairwise trials and four Latin square trials were conducted across three peri-urban sites, comprising two saltwater sites and one freshwater site, in southeast Queensland, Australia. In all trials, CO2-baited traps outperformed traps baited with cyclopentanone. Carbon dioxide-baited CDC traps collected significantly more total mosquitoes, Aedes vigilax (Skuse), Culex sitiens Weidemann, and Culex annulirostris Skuse, than those baited with ≥99% cyclopentanone in pairwise trials. Similarly, in almost all Latin square trials, CO2-baited CDC and CFG traps collected significantly greater numbers of total mosquitoes, Ae. vigilax, Cx. annulirostris, Culex orbostiensis Dobrotworsky, and Cx. sitiens when compared with CFG traps baited with 20% cyclopentanone. Our trials indicate that cyclopentanone is not effective as a mosquito attractant in the field and cannot be used as a simple substitute for CO2 in commonly used mosquito surveillance traps.

Aedes albopictus (Diptera: Culicidae) as a potential vector of endemic and exotic arboviruses in Australia.

In 2005, established populations of Aedes albopictus (Skuse) were discovered in the Torres Strait, the region that separates Papua New Guinea from northern Australia. This increased the potential for this species to be introduced to mainland Australia. Because it is an arbovirus vector elsewhere, we undertook laboratory-based infection and transmission experiments to determine the potential for Ae. albopictus from the Torres Strait to become infected with and transmit the four major Australian endemic arboviruses--Murray Valley encephalitis virus, West Nile virus Kunjin strain (WNV(KUN)), Ross River virus (RRV), and Barmah Forest virus--as well as the exotic Japanese encephalitis virus. Ae. albopictus is susceptible to infection with all viruses, with infection rates ranging between 8% for WNV(KUN) and 71% for RRV. Transmission rates of approximately 25% were observed for RRV and Barmah Forest virus, but these were < 17% for Murray Valley encephalitis virus, WNV(KUN), and Japanese encephalitis virus. Given its relative vector competence for alphaviruses, we also examined the replication kinetics and extrinsic incubation periods required for transmission of RRV and chikungunya virus. Despite lower body titers, more mosquitoes reared and maintained at 28 degrees C became infected with and transmitted the virus than those reared and maintained at 22 degrees C. The minimum time between Ae. albopictus consuming an infected bloodmeal and transmitting chikungunya virus was 2 d at 28 degrees C and 4 d at 22 degrees C, and for RRV, it was 4 d, irrespective of the temperature. Given its opportunistic feeding habits and aggressive biting behavior, the establishment of Ae. albopictus on the Australian mainland could have a considerable impact on alphavirus transmission.

Ability for Aedes albopictus (Diptera: Culicidae) to survive at the climatic limits of its potential range in eastern Australia.

Aedes albopictus (Skuse) is one of the most invasive mosquito species in the world and has infested islands in the Torres Strait, off the northern coast of Australia since at least 2004. This has led to fears that it may establish on the Australian mainland, including highly populated cities in southern temperate regions. To supplement theoretical projections addressing the range expansion of Ae. albopictus into Australia, laboratory-based trials were conducted to assess the performance of a Torres Strait Ae. albopictus population under a range of Australian conditions. First-instar larvae were placed in individual microcosms and maintained on a natural food resource, under average climatic conditions representing different regions of Australia's east coast. Larvae could not survive winter conditions in southern Australia. As the population performance index was >1.0 for tropical winter and summer conditions, and temperate summer conditions, populations would likely increase during these times. To test whether Ae. albopictus could overwinter during adverse conditions as eggs, we exposed cohorts to four different temperature (7, 17, 27, and 33 degrees C) and relative humidity (35, 55, and 80%) combinations for up to 3 mo. High temperatures and low humidity were most detrimental to egg survival. However, those eggs maintained under cooler climates remained viable after 3 mo, including 17% of eggs kept at 7 degrees C. Overall, this study suggests that a Torres Strait Ae. albopictus strain could proliferate all year round under northern tropical conditions and could overwinter in the egg stage before proliferating in the summer in southern temperate regions.

Emerging tropical diseases in Australia. Part 5. Hendra virus.

Hendra virus (HeV) was first isolated in 1994, from a disease outbreak involving at least 21 horses and two humans in the Brisbane suburb of Hendra, Australia. The affected horses and humans all developed a severe but unidentified respiratory disease that resulted in the deaths of one of the human cases and the deaths or putting down of 14 of the horses. The virus, isolated by culture from a horse and the kidney of the fatal human case, was initially characterised as a new member of the genus Morbillivirus in the family Paramyxoviridae. Comparative sequence analysis of part of the matrix protein gene of the virus and the discovery that the virus had an exceptionally large genome subsequently led to HeV being assigned to a new genus, Henipavirus, along with Nipah virus (a newly emergent virus in pigs). The regular outbreaks of HeV-related disease that have occurred in Australia since 1994 have all been characterised by acute respiratory and neurological manifestations, with high levels of morbidity and mortality in the affected horses and humans. The modes of transmission of HeV remain largely unknown. Although fruit bats have been identified as natural hosts of the virus, direct bat-horse, bat-human or human-human transmission has not been reported. Human infection can occur via exposure to infectious urine, saliva or nasopharyngeal fluid from horses. The treatment options and efficacy are very limited and no vaccine exists. Reports on the outbreaks of HeV in Australia are collated in this review and the available data on the biology, transmission and detection of the pathogen are summarized and discussed.

Emerging tropical diseases in Australia. Part 4. Mosquitoborne diseases.

Mosquito-borne diseases continue to be a serious public-health concern in Australia. Endemic alphaviruses (including Ross River and Barmah Forest viruses) account for the majority of the arboviral notifications, while some flaviviruses (Murray Valley encephalitis, Japanese encephalitis and Kunjin viruses) cause occasional outbreaks of encephalitis. Dengue epidemics are increasing in frequency in northern Queensland, with the largest outbreak in 50 years occurring during the 2008-2009 wet season. Of great concern are the threats posed by the importation of exotic arboviruses, such as West Nile, chikungunya and Rift Valley fever viruses, the introduction of exotic vectors, and the potential range expansion of key Australian vectors. Environmental and anthropogenic influences provide additional uncertainty regarding the future impact of mosquito-borne pathogens in Australia. This review discusses the trends, threats and challenges that face the management of mosquito-borne disease in Australia. Topical mosquito-borne pathogens of biosecurity and public-health concern, and the potential impacts of environmental and global trends, are discussed. Finally, a short overview of the public-health response capability in Australia is provided.

Emerging tropical diseases in Australia. Part 1. Leptospirosis.

Human leptospirosis is a zoonotic disease of global importance that causes significant morbidity and mortality, particularly in developing nations. In this review, the history, epidemiology, transmission, clinical presentation and treatment of this disease, and its impact in Australia, are discussed. Central to this review is the delineation of diagnostic methods for the disease and the challenges that this disease presents for both the clinician and diagnostic laboratory. This information should furnish clinicians with an updated tool to help overcome a number of problems associated with the diagnosis of leptospirosis.

No Evidence of Hendra Virus Infection in the Australian Flying-fox Ectoparasite Genus Cyclopodia.

Hendra virus (HeV) causes potentially fatal respiratory and/or neurological disease in both horses and humans. Although Australian flying-foxes of the genus Pteropus have been identified as reservoir hosts, the precise mechanism of HeV transmission has yet to be elucidated. To date, there has been limited investigation into the role of haematophagous insects as vectors of HeV. This mode of transmission is particularly relevant because Australian flying-foxes host the bat-specific blood-feeding ectoparasites of the genus Cyclopodia (Diptera: Nycteribiidae), also known as bat flies. Using molecular detection methods, we screened for HeV RNA in 183 bat flies collected from flying-foxes inhabiting a roost in Boonah, Queensland, Australia. It was subsequently demonstrated that during the study period, Pteropus alecto in this roost had a HeV RNA prevalence between 2 and 15% (95% CI [1, 6] to [8, 26], respectively). We found no evidence of HeV in any bat flies tested, including 10 bat flies collected from P. alecto in which we detected HeV RNA. Our negative findings are consistent with previous findings and provide additional evidence that bat flies do not play a primary role in HeV transmission.

Flaviviruses isolated from mosquitoes collected during the first recorded outbreak of Japanese encephalitis virus on Cape York Peninsula, Australia.

In response to an outbreak of Japanese encephalitis (JE) virus on Cape York Peninsula, Australia, in 1998, mosquitoes were collected using CO2 and octenol-baited Centers for Disease Control and Prevention light traps. A total of 35,235 adult mosquitoes, comprising 31 species, were processed for virus isolation. No isolates of JE virus were recovered from these mosquitoes. However, 18 isolates of Kokobera virus, another flavivirus were obtained from Culex annulirostris. Twelve isolates were from western Cape York (minimum infection rate (MIR) of 0.61: 1,000 mosquitoes) and 6 were from the Northern Peninsula Area (MIR of 1.0:1,000). Potential explanations for the failure to detect JE virus in mosquitoes collected from Cape York Peninsula include the timing of collections, the presence of alternative bloodmeal hosts, differences in pig husbandry, asynchronous porcine seroconversion, and the presence of other flaviviruses.

Isolation of Japanese encephalitis virus from mosquitoes (Diptera: Culicidae) collected in the Western Province of Papua New Guinea, 1997-1998.

After Japanese encephalitis (JE) virus emerged in the Torres Strait in Australia in 1995, investigations were initiated into the origin of the incursion. New Guinea was considered the most likely source, given its proximity to islands of the Torres Strait. Almost 400,000 adult mosquitoes were processed for virus isolation from 26 locations in the Western Province of Papua New Guinea (PNG) between February 1996 and February 1998, yielding three isolates of JE virus. Two isolates of Murray Valley encephalitis, 17 isolates of Sindbis, and 1 each of Sepik and Ross River viruses were also obtained. Nucleic acid sequences of the PNG JE isolates were determined in the prM region, and in a region overlapping a part of the fifth nonstructural protein and the 3' untranslated region. The PNG isolates belonged to genotype II, and shared > 99.2% identity with isolates from humans and mosquitoes from the Torres Strait, suggesting that PNG is the source of incursions of JE virus into Australia.

The appearance of a second genotype of Japanese encephalitis virus in the Australasian region.

In mid-January 2000, the reappearance of Japanese encephalitis (JE) virus activity in the Australasian region was first demonstrated by the isolation of JE virus from 3 sentinel pigs on Badu Island in the Torres Strait. Further evidence of JE virus activity was revealed through the isolation of JE virus from Culex gelidus mosquitoes collected on Badu Island and the detection of specific JE virus neutralizing antibodies in 3 pigs from Saint Pauls community on Moa Island. Nucleotide sequencing and phylogenetic analyses of the premembrane and envelope genes were performed which showed that both the pig and mosquito JE virus isolates (TS00 and TS4152, respectively) clustered in genotype I, along with northern Thai, Cambodian, and Korean isolates. All previous Australasian JE virus isolates belong to genotype II, along with Malaysian and Indonesian isolates. Therefore, for the first time, the appearance and transmission of a second genotype of JE virus in the Australasian region has been demonstrated.

Japanese encephalitis on Badu Island, Australia: the first isolation of Japanese encephalitis virus from Culex gelidus in the Australasian region and the role of mosquito host-feeding patterns in virus transmission cycles.

During investigation of an outbreak of Japanese encephalitis (JE) in the Torres Strait, Australia, in 2000, mosquitoes were collected in Badu Island community and at a newly established communal piggery about 3 km from the community. A total of 94,285 mosquitoes, comprising 91,240 (96.8%) unengorged females, 1630 (1.7%) blood-engorged females and 1415 (1.5%) males, were processed for virus isolation. One isolate of JE virus was obtained from Culex gelidus, with a minimum infection rate of 12.4:1000. This is the first isolate of JE virus from Cx. gelidus in the Australasian region. No isolates were obtained from Cx. annulirostris, the primary implicated Australian JE vector. Analysis of mosquito host-feeding patterns, using gel diffusion, demonstrated that Cx. annulirostris and 5 other species fed predominately on mammals. Analysis of blood-fed mosquitoes collected within the community demonstrated that the proportion of Cx. annulirostris feeding on pigs in 2000 (2.3%) was significantly lower than that for the 1995-97 period (31.3%). The removal of the pigs from Badu Island community has limited the contact between potential amplifying hosts and mosquitoes, thus potentially reducing the risk of transmission of JE virus to the human population.

Definition of species in the Culex sitiens subgroup (Diptera: Culicidae) from Papua New Guinea and Australia.

Japanese encephalitis is a disease of major importance in Asia, which from 1995 has extended its range into the north of Australia. Culex annulirostris Skuse of the Culex sitiens subgroup of Culex was incriminated as the most likely mosquito vector. Because misidentifications previously have occurred within this subgroup, our paper defines electrophoretic methods to identify Culex specimens from Queensland and the Northern Territory in Australia and from Western Province in Papua New Guinea. In collections from 1996 to 1998 Culex sitiens Wiedemann, Cx. palpalis Taylor, and Cx. annulirostris comprised 93.1% of the total banded proboscis Culex mosquitoes collected; 6.9% remained unidentified to species by morphological or electrophoretic examination. The prevalence of Cx. palpalis was variable and appeared to be associated with below average rainfall during 1997. In Papua New Guinea, this species comprised up to 97.4% of banded proboscis Culex, with smaller numbers collected from the Torres Strait Islands and Cape York; none was collected from other Queensland localities. Cx. annulirostris was more prevalent during years of average or above average rainfall and was predominant in most localities, especially in the Torres Strait and Queensland. These data confirmed the problems in separating Cx. sitiens from Cx. palpalis and Cx. annulirostris using morphological characters.

Seasonal abundance of Anopheles farauti (Diptera: Culicidae) sibling species in far north Queensland, Australia.

In the Cairns area of far north Queensland, Australia, the seasonal abundance of Anopheles farauti Laveran sibling species was studied at 6 locations, representing 3 habitat types, between August 1995 and September 1997. A total of 45,401 An. farauti s.l. was collected using CO2 + octenol baited CDC light traps, and consisted of 29,565 An. farauti No. 2, 14,214 An. farauti No. 3, and 1,622 An. farauti s.s. The relative abundance of all 3 species differed significantly by season and location. An. farauti No.2 was the dominant species except in Cairns, where An. farauti s.s. was most abundant, and at Ninds Creek, where An. farauti No. 3 predominated. The dominant species at each location was present year round, although peaks in seasonal abundance were observed. An. farauti s.s. populations were highest during the wet season (January-April). In lowland freshwater swamp habitats and 1 brackish location, An. farauti No. 2 was more abundant during the wet season. However, at the highland freshwater swamp habitat, populations of An. farauti No. 2 were highest during the late dry season and early wet season (October-December). There was a significant positive correlation of both temperature and rainfall with An. farauti s.s. and An. farauti No. 2 trap collections. There was a negative correlation between An. farauti No. 3 and temperature, indicating that this species may be more abundant during cool weather. Although there were significant relationships among weather variables and An. farauti s.l. collections, correlation values were generally low, indicating that other factors may contribute to variability among An. farauti sibling species trap collections.

Development and evaluation of a species diagnostic polymerase chain reaction-restriction fragment-length polymorphism procedure for cryptic members of the Culex sitiens (Diptera: Culicidae) subgroup in Australia and the southwest Pacific.

Members of the Culex sitiens subgroup are important vectors of arboviruses, including Japanese encephalitis virus, Murray Valley encephalitis virus and Ross River virus. Of the eight described species, Cx. annulirostris Skuse, Cx. sitiens Wiedemann, and Cx. palpalis Taylor appear to be the most abundant and widespread throughout northern Australia and Papua New Guinea (PNG). Recent investigations using allozymes have shown this subgroup to contain cryptic species that possess overlapping adult morphology. We report the development of a polymerase chain reaction-restriction fragment-length polymorphism (PCR-RFLP) procedure that reliably separates these three species. This procedure utilizes the sequence variation in the ribosomal DNA ITS1 and demonstrates species-specific PCR-RFLP profiles from both colony and field collected material. Assessment of the consistency of this procedure was undertaken on mosquitoes sampled from a wide geographic area including Australia, PNG, and the Solomon Islands. Overlapping adult morphology was observed for Cx. annulirostris and Cx. palpalis in both northern Queensland and PNG and for all three species at one site in northwest Queensland.

Vector competence of Australian mosquitoes (Diptera: Culicidae) for Japanese encephalitis virus.

Australian mosquitoes were evaluated for their ability to become infected with and transmit a Torres Strait strain of Japanese encephalitis virus. Mosquitoes, which were obtained from either laboratory colonies and collected using Centers for Disease Control and Prevention light traps baited with CO2 and octenol or reared from larvae, were infected by feeding on a blood/sucrose solution containing 10(4.5 +/- 0.1) porcine stable-equine kidney (PS-EK) tissue culture infectious dose50/mosquito of the TS3306 virus strain. After 14 d, infection and transmission rates of 100% and 81%, respectively, were obtained for a southeast Queensland strain of Culex annulirostris Skuse, and 93% and 61%, respectively, for a far north Queensland strain. After 13 or more days, infection and transmission rates of > 90% and > or = 50%, respectively, were obtained for southeast Queensland strains of Culex sitiens Wiedemann and Culex quinquefasciatus Say, and a far north Queensland strain of Culex gelidus Theobald. Although infection rates were > 55%, only 17% of Ochlerotatus vigilax (Skuse) and no Cx. quinquefasciatus, collected from far north Queensland, transmitted virus. North Queensland strains of Aedes aegypti L., Ochlerotatus kochi (Dönitz), and Verrallina funerea (Theobald) were relatively refractory to infection. Vertical transmission was not detected among 673 F1 progeny of Oc. vigilax. Results of the current vector competence study, coupled with high field isolation rates, host feeding patterns and widespread distribution, confirm the status of Cx. annulirostris as the major vector of Japanese encephalitis virus in northern Australia. The relative roles of other species in potential Japanese encephalitis virus transmission cycles in northern Australia are discussed.

Entomological investigations of an outbreak of Japanese encephalitis virus in the Torres Strait, Australia, in 1998.

Japanese encephalitis (JE) virus first appeared in Australia in 1995, when three clinical cases (two fatal) were diagnosed in residents on Badu Island in the Torres Strait, northern Queensland. More recently, two confirmed human JE cases were reported in the Torres Strait Islands and Cape York Peninsula, in northern Queensland in 1998. Shortly after JE virus activity was detected in humans and sentinel pigs on Badu Island in 1998, adult mosquitoes were collected using CO2 and octenol-baited CDC light traps; 43 isolates of JE virus were recovered. Although Culex sitiens group mosquitoes yielded the majority of JE isolates (42), one isolate was also obtained from Ochlerotatus vigilax (Skuse). Four isolates of Ross River virus and nine isolates of Sindbis (SIN) virus were also recovered from members of the Culex sitiens group collected on Badu Island in 1998. In addition, 3,240 mosquitoes were speciated and pooled after being anesthetized with triethylamine (TEA). There was no significant difference in the minimum infection rate of mosquitoes anesthetized with TEA compared with those sorted on refrigerated tables (2.8 and 1.6 per 1,000 mosquitoes, respectively). Nucleotide analysis of the premembrane region and an overlapping region of the fifth nonstructural protein and 3' untranslated regions of representative 1998 Badu Island isolates of JE virus reveled they were identical to each other. Between 99.1% and 100% identity was observed between 1995 and 1998 isolates of JE from Badu Island, as well as isolates of JE from mosquitoes collected in Papua New Guinea (PNG) in 1997 and 1998. This suggests that the New Guinea mainland is the likely source of incursions of JE virus in Australia.

Isolation of arboviruses from mosquitoes (Diptera: Culicidae) collected from the Gulf Plains region of northwest Queensland, Australia.

As part of investigations into Japanese encephalitis (JE) virus and related flaviviruses in northern Australia, 153,529 mosquitoes were collected and processed for virus isolation from the Gulf Plains region of northwest Queensland. Collections from within 30 km of each of the townships of Croydon, Normanton and Karumba yielded 3,087 (2.0%), 66,009 (43.0%), and 84,433 (55.0%) mosquitoes, respectively, from which 16 viruses were isolated. Four isolates of Murray Valley encephalitis (MVE), two of Kunjin (KUN), three of Ross River (RR), and one of Sindbis (SIN) viruses were obtained from Culex sitiens subgroup mosquitoes. Molecular identification of the mosquito species composition of these virus positive pools revealed that most isolates were from pools containing mainly Culex annulirostris Skuse and low numbers of Culex palpalis (Taylor). Only three pools, one each of MVE, KUN, and RR, were from mosquitoes identified exclusively as Cx. annulirostris. Other viruses isolated include one Edge Hill virus from Ochlerotatus normanensis (Taylor), an isolate of SIN from Anopheles meraukensis Venhuis, two isolates of RR from Anopheles amictus Edwards, and single isolates of RR from Anopheles bancroftii Giles andAedes lineatopennis (Ludlow). The isolate of RR from Ae. lineatopennis was the first reported from this species. The public health implications of these isolations in the Gulf Plains region are discussed briefly.

Malaria and its implications for public health in Far North Queensland: a prospective study.

This prospective study's objectives were to describe the features of all episodes of malaria diagnosed in Far North Queensland (excluding the Torres Strait) and to assess how much of a threat they posed to the area's public health. Over a three-year period, 216 episodes of malaria were diagnosed (158 Plasmodium vivax and 68 P. falciparum infections). Most (82%) of the infections were acquired in Papua New Guinea (PNG). Approximately 70% of the episodes occurred in Australian citizens, about half of whom were in malaria-endemic countries for work; the remainder travelled abroad for recreation. Three-quarters of the Australian citizens with malaria had taken either no or inadequate prophylaxis. Australian citizens who had taken adequate prophylaxis were much less likely to develop P. falciparum than other types of malaria compared to those who took either no or inadequate prophylaxis (p = 0.01). Gametocytes were present in 121 (56%) of the episodes of malaria. Mosquito surveillance was carried out in response to 38 (31%) of these gametocytaemic episodes. Significant numbers of Anopheles farauti sensu lato mosquitoes were found close to the residence of a patient in 4 (11%) of these episodes. Only two occasions when local transmission could have possibly occurred were recognised. We do not believe malaria poses an important threat to the health of the public in Far North Queensland. Nevertheless, it remains an important problem for those who travel abroad to malarious areas.